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Enhancement of the magnetic susceptibility of pyrite particles is observed following a mild oxidative pressure leach. This increase is studied for a range of experimental conditions. The increase in susceptibility is attributed to the formation of a thin layer of ferromagnetic oxides. This layer of leach reaction products has been extensively studied using various analytical techniques. The species identified are (gamma)-Fe(,2)O(,3) and Fe(,3)O(,4), which supports a previously postulated reaction model. / This leach treatment significantly increases the magnetic susceptibility of coal-pyrite permitting improved high-gradient magnetic desulfurization of a high pyritic sulfur coal. / The leach treatment also enhances the magnetic susceptibility of other iron-containing mineral sulfides. However, application of this leach pretreatment in sulfide/sulfide separations is limited due to galvanic coupling effects which passivate the susceptibility increase reaction. In the presence of oxides, coal and probably other non-sulfides passivation does not occur and the susceptibility of the iron-bearing sulfide increases. The potential exists for the application of the leach as a pretreatment in enhancing fine iron-containing sulfide/non-sulfide magnetic separations.

The behavior of model three phase solid/liquid/liquid systems has been studied in the external fields of shear or gravity. Observations of the deformation and break-up of solid-liquid clusters in a simple shear field has led to an investigation of various aspects of separation and coalescence phenomena: the interaction of solid particles and drops in simple shear, film thinning processes, the thermodynamics of engulfment and solid-liquid separation by the external fields. / A microrheological approach was used to determine which parameters are important to the behavior of these systems in simple shear. Among the most important were found to be the liquid/liquid interfacial tension, the incidence of three phase contact and/or the wettability of the solid surface. / The importance of these paramters was also investigated in the formation and stability of sphere-drop systems in a gravitational field, and the detachment of the liquid drop by surface and gravitational forces. / Extensions to existing theory have been made to include gravitational effects in the thinning of a liquid film which forms around a sphere. Finally, an asymptotic solution to the Laplace equation of capillarity has been developed which may be applied to various axisymmetric liquid/fluid interfaces not too far from spherical shape. / The findings in this thesis are highly relevant to various industrial processes (such as in the production of oil, minerals, paper, etc.) where three phase systems are encountered.